ns compared with that of the present day. 77 



number of species still to be discovered will equal in amount that of 

 the so-called species, which, being founded on imperfect specimens, 

 will ultimately prove to belong to previously-described forms. 



That the vegetation of the carboniferous period, whether confined 

 to the coal veins or not, was highly luxuriant, cannot be disputed. 

 The enormous bulk of carbon accumulated, and the prevalence of 

 ferns in all the fields, and the great size to which so many soft-tis- 

 sued plants attained, all prove this fact. A luxuriant vegetation is, 

 however, no index to a varied one ; and, as many of our modern 

 woods, and even great arese of tropical forests, consist of but a hvf 

 species multiplii'd ad infinitum, so may the forests of the carbonife- 

 rous period have been composed of but a few SigillaricB and Lepido- 

 dendronSy sheltering an under growth of a limited number of kinds 

 of fern,* for a very limited number of them {comparatively speaking), 

 if as protean as some of their allies are in our day, would embrace 

 all the known species of the Fossil Flora. 



In the temperate latitudes particularly, a recent Flora, marked by 

 a preponderance of ferns, is almost universally deficient in species 

 other orders ; as is thus shewn. 1. Where one species prevails over 

 a considerable area, as the bracken {Pteris aquilina) does in parts 

 of Britain, and the P. esculenta in Van Diemen's Land and New 

 Zealand, it generally monopolises the soil, choking plants of a larger 

 growth on the one hand, and admitting no undergrowth of smaller 

 species on the other. 2. A luxuriant vegetation of many species of 

 ferns, continued through a great many degrees of latitude or longi- 

 tude, especially in the temperate regions of the globe, generally indi- 

 cates a uniformity of temperature throughout that area, and a paucity 

 of species of flowering plants. A comparison of the vegetations of 

 Tasmania and New Zealand illustrates this. The former of these 

 islands, barely 200 miles long, contains four times as many species 

 of flowering plants as New Zealand, whose total length is 900 miles. 

 On the other hand, this latter country possesses more than four times 

 as many kinds of fern as Tasmania, and they are so uniformly dis- 

 tributed over its area, that almost all those which are found at the 

 southern extremity of the island, prevail also at the northern. The 

 West Indian and Pacific Islands again present a flora, remarkably 

 rich in ferns, and, in both these instances, we have very many of the 

 species uniformly spread over an enormous surface, in the one in- 

 stance, from the Windward Islands to Mexico ; and, in the other, 



* This preponderance of ferns over flowering plants is common to many tro- 

 pical islands, and not confined to the smaller of them, as St Helena and the So- 

 ciety group. In extratropical islands, too, as New Zealand, I have collected 

 as many as thirty-six kinds of fern in an area not exceeding a few acres ; they 

 gave a most luxuriant aspect to the vegetation, which presented scarcely a 

 dozen flowering plants and trees besides. An equal area in the neighbourhood 

 of Sydney (in about the same latitude), would have yielded upwards of 100 

 flowering plants, and but two or three ferns. 



